How the Macro Calculator Works
Most macro calculators split your calories into fixed percentages — say 40/30/30. The problem is that protein needs scale with your body, not your calories: a 50 kg person and a 100 kg person eating 2,000 kcal would get the same protein. This calculator sets protein by body weight first, protects a minimum amount of fat, and gives the rest of your calories to carbs.
Step 1: Your calories
If you choose Estimate, your resting energy needs come from the Mifflin–St Jeor equation, multiplied by your activity level to get maintenance calories. Your goal then adjusts that number.
Men: (10 × kg) + (6.25 × cm) − (5 × age) + 5
Women: (10 × kg) + (6.25 × cm) − (5 × age) − 161
Maintenance = result × activity factor (1.2 – 1.9)
| Goal | Calories | Protein (lifting) | Protein (not lifting) |
|---|
| Lose fat | ≈ 20% below maintenance | 2.0 g/kg | 1.6 g/kg |
| Lose fat slowly | ≈ 10% below | 2.0 g/kg | 1.6 g/kg |
| Recomposition | ≈ 5% below | 2.0 g/kg | 1.6 g/kg |
| Maintain | Maintenance | 1.6 g/kg | 1.2 g/kg |
| Lean muscle gain | ≈ 10% above | 1.8 g/kg | 1.6 g/kg |
Step 2: Protein, fat, then carbs
Protein g = g/kg × reference weight → × 4 kcal
Fat g = (fat % × calories) ÷ 9, never below 0.6 g/kg
Carbs g = (calories − protein kcal − fat kcal) ÷ 4
If your BMI is above 30, protein is based on the weight you'd be at a BMI of 27 rather than your current weight — otherwise targets can climb far beyond what's useful. Read more in How Much Protein Do You Actually Need?
Step 3: Split it across your meals
Spreading protein fairly evenly across meals — rather than loading it all into dinner — tends to support muscle better. Around 0.4 g per kg per meal is a useful marker. See how to distribute protein across your day.
How to use your numbers
- Hit protein and calories first. Carbs and fat can flex a little from day to day.
- Give it two to three weeks. Track your weight trend, not single weigh-ins, before changing anything.
- Adjust by 100–200 kcal if you're not moving in the direction you want — usually from carbs or fat, not protein.
- Don't chase precision. Being within about 10% most days works. If tracking every gram feels stressful, read why calorie counting doesn't work for everyone.
Frequently Asked Questions
How does this macro calculator work out my macros?
It starts with your daily calories — either estimated from your age, sex, height, weight and activity using the Mifflin–St Jeor equation, or a number you already know. It then sets protein in grams per kilogram of body weight for your goal, sets fat as a share of calories with a minimum of about 0.6 g per kg, and gives the remaining calories to carbohydrates. Protein and carbs count as 4 calories per gram, fat as 9.
How much protein do I need per day?
For people who do resistance training, research supports roughly 1.6 to 2.2 g of protein per kg of body weight per day, with the higher end most useful during a calorie deficit. This calculator uses 1.6 g/kg for maintenance, 1.8 g/kg for lean gain and 2.0 g/kg for fat loss or recomposition. If you don't lift weights, it uses lower targets of 1.2 to 1.6 g/kg.
Should I count macros or just calories?
Calories decide whether your weight goes up or down; macros shape what that weight is made of and how you feel. If you only track one thing beyond calories, make it protein — it protects muscle in a deficit and keeps you fuller. Carbs and fat can flex day to day as long as your total calories and protein land close to target.
What is the best macro split for fat loss?
There is no single best split. Studies comparing higher-carb and lower-carb diets at the same calories and protein show similar fat loss. What matters most is a moderate calorie deficit, enough protein and a split you can stick to. That's why this calculator fixes protein by body weight and lets you choose balanced, higher-carb or lower-carb for the rest.
How accurate is a macro calculator?
Calorie estimates from equations are usually within about 10% for most people, but individuals vary. Treat your numbers as a starting point: follow them consistently for two to three weeks, track your weight trend, then adjust calories by 100 to 200 a day if you are not moving in the direction you want.
Disclaimer: This calculator gives general estimates for healthy adults and is not medical or dietary advice. If you are pregnant or breastfeeding, under 18, have a medical condition such as diabetes or kidney disease, or have a history of disordered eating, talk to a doctor or registered dietitian before changing how you eat.